Core constructions



March 28, 1961 A. R. CORNELL EIAL 2,977,555

CORE CONSTRUCTIONS Filed Jan. 28, 1955 2 Sheets-Sheet 2 64 65 Fig.4.

||||||||| llll illlllllllllllllllll United States Patent CORE CONSTRUCTIONS Filed Jan. 28, 1955, Sen-No. 484,742 8 Claims. (Cl. 33616'5) and Burton A. Wyman, assignors to Westinghouse Electric East Pittsburgh, Pa., 'a corporation of Our invention relates generally to core constructions and, more particularly, to core constructions such as are employed for the transformer and ballast coils used for the control of one or more gaseous discharge devices having negative resistance characteristics, such as fluorescent lamps.

In constructing transformer cores for controlling gaseous discharge devices, such as fluorescent lamps, it has been common practice to make the laminations for the core from two or more pieces of magnetic sheet material having a fixed magnetic circuit; the circuit may consist of shunts and/or air gaps between the portions of the core, upon which the primary and secondary windings are located. Such magnetic shunts are often formed integral with one portion of the core and spaced from another portion of the core to provide an air gap in the core. Also, such transformer cores are usually stamped from thin magnetic sheet material, and with such material considerable diiiiculty has been experienced in obtaining one or more narrow ai-r gaps between the various portions of the core. As can also be appreciated, it is highly desirable in such control transformers that all of the necessary control coils be mounted on a single core construction in order to reduce the material cost of the cores and the number and weight of the components needed in a particular control circuit. With common types of cores considerable difiiculty is encountered in providing means whereby the reluctance between the portions of the core may be manually varied after the core is assembled. Still again it is desirable that such core constructions be capable of being fabricated with as little scrap loss as possible in order to reduce the material cost of the core.

Accordingly, one object of our invention is to provide a new and improved two-piece core construction of the type described, having means for movably supporting one part of the core in the same plane as the other part of the core and in. an infinite number of positions in one direction relative to the other part of the core.

Another object of our invention is to provide a new and improved two-piece elongated core construction of the type described, which has one part movably supported at each of its ends by the other part, so that the reluctance of the core may be varied by moving the one part longitudinally with relation to the other part and still support both ends of the movable part.

Another object of our invention is to provide a new and improved two-piece core construction of the type described comprising an elongated U-shaped member-having an elongated I-shaped member located between the arms of the U-shaped member and with the I-shaped member having means engagcable with the base of the U-shaped member, so that the I-shaped member may be movably supported in an infinitely number of positions in one direction with respect to the U-shaped member.

Another object of our invention is to provide a new and improved two-piece core construction of the type described having an elongated winding leg portion and an elongated yoke portion with magnetic shunts adjacent the winding leg portion and with the winding leg portion being supported at each of its ends by' the yoke portion and being'longitudinally movable in various positions with respect to the yoke without substantially affecting the shunt air gaps or the support of the winding leg portion by the yoke portion.

Still another object of our invention is to provide a new and improved two-piece core construction of the type described comprising two parts which may economically be fabricated from a single piece of material, and which may be located in a plurality of positions with respect to each other.

A more specific object of our invention is to provide a new and improved-two-piece core construction of the type described having an elongated I-shaped member which is centrally located between the arms of the elongated U- shaped member which are cooperable in a novel manner.

Another object of our invention is to provide a new and improved elongated two-piece core construction of the type described comprising, two parts which are fabricated from a single piece of material so as to be mechanically separated from each other with one part thereof being rotatable around its longitudinal axis so as to obtain certain magnetic characteristics.

These and other objects of our invention will become more apparent upon consideration of the following detailed description of the preferred embodiments thereof when taken in conjunction with the attached drawings, in which:

Figure l is a plan view of one type of core lamination constructed in accordance with the principles of our invention as it appears immediately after its initial blanking operation;

Fig. 2 is an enlarged plan view of a section of the core lamination shown in Fig. 1 showing the inner end of the Winding leg displaced longitudinally from the yoke;

Fig. 3 is a plan view of another type of core lamination constructed in accordance with the principles of our invention with the winding leg as it appears after being relocated within the yoke;

Fig, 4 is a top plan view of a transformer assembly having core laminations as shown in Fig. l, which illustrates a gaseous discharge device connected thereto;

Fig. 5 is a side elevational view of the transformer shown in Fig. 4; and

Fig. 6 is an end elevational view of the transformer shown in Fig. 4.

The core structures constructed in accordance with the principles of this invention, examples of which are specifically hereinafter described, are all adapted to be built up of a plurality of laminations with eachlamination comprising only two parts which may be stamped out of a single sheet of magnetic material. This is achieved in accordance with this invention by stamping out the two parts of the core in such relationship that very close control is maintained of the parts which formv magnetic shunts in the assembled core structure while retaining provisions for some adjustment of the reluctance of the core.

Referring first to Fig. 4 of the drawings, it will be noted that each lamination of the core constructed in accordance with the principles of our invention comprises a flat elongated U-shaped yoke 2 having a bight portion 4 which connects substantially identically formed, longitudinally extending arms 6. A flat elongated substantially rectangular winding leg 8 is located between the arms 6 of the yoke 2. As shown, the winding leg 8 extends from the inner side of bight portion 4 to the outer ends of arms 6 so as to be substantially fiush therewith. In order to support the winding leg 8 adjacent-the free end of each arm 6, the :free end of each arm 6 is provided with a laterally inwardly extending projection which engages opposite sides of the winding leg 8. The other end of winding leg 8 is supported between the arms 6 of the yoke 2 by providing the end of winding leg 8 ad jacent the bight portion 4 of yoke 2 with a longitudinally outwardly extending projection 12 which is located so as to be in engagement with a substantially identically contoured recess or notch 14 in the inner side of bight portion 4. By such construction, winding leg 8 is supported at each of its ends so that each side thereof is spaced from the inner side of the adjacent arms 6.

For the purposes of our invention, a pair of separate coils 18 and 20 (Fig. 4) are located in spaced relationship along winding leg 8 with portions thereof located between winding leg 8 and yoke 2. Coils 18 and 20 are wound separately in any manner well known in the art of any suitable electrical conducting material, such as copper wire, and which are electrically connected together in any suitable manner, such as by a conductor 22 so as to be in autotransformer relationship when connected to load and supply circuits as hereinafter indicated. As shown, coil 18 is located with its outer side closely adjacent projections 10, secondary coil 20 is located with its outer side closely adjacent the bight portion 4 of yoke 2, and the inner sides of the coils 18 and 20 are spaced from each other. In order to permit winding leg 8 to be rotated with respect to the arms 6 of yoke 2, as hereinafter described, the longitudinal center line of Winding leg 8 corresponds to the longitudinal center line of the yoke 2.

A magnetic shunt is provided between the coil 18 and coil 20 which comprises a transversely outwardly extending projection 24A extending from the upper side of winding leg 8 and a projection 24B extending from the lower side of Winding leg 8. It will be noted that projection 24A is spaced from the upper arm 6 and that the lower arm 6 is provided with a transversely inwardly extending projection 26 opposite projection 24B, in order that the air gap between projection 26 and projection 24B is substantially equal to the air gap between the projection 24A and the upper arm 6 of yoke 2, as is more fully described hereinafter.

It will be noted that the core construction described above is particularly adapted to be fabricated from a single piece of material and preferably is formed froin long sheets or strips of material, so that a number of laminations may be punched in tandem. Fig. 1 illustrates As has been indicated, fabricating a narrow air gap in a lamination is quite diflicult and in keeping with the principles of our invention, it' will be noted that although the finished core is provided with two air gaps, as shown in Fig. 4, only the projection 24B, as shown in Fig. 1, is spaced from the adjacent arm 6 of the yoke 2 during the preceding operation. Thus, in blanking the lamina tion, only one air gap is fabricated which is equal in width to the total desired width of both air gaps in the completed core. Although the single air gap formed in the punching operation (Fig. l) is of a small length, the increase in length over forming two individual air gaps of the smaller size used in the finished core (Fig. 4) greatly facilitates the blanking of the core. Primarily the greater air gap width permits the use of a Wider punch which is stronger than a narrower punch whereby the punch life is increased. Also, the punching of a a single lamination as it is punched out and before it is rearranged to form the core structure of Fig. 4. It will be noted that each projection 10 is provided with a longitudinally inwardly projecting notch 30 which, when the laminations are formed in tandem, forms a projection 32 on the bight portion 4 adjacent each arm 6 which extends longitudinally outwardly therefrom. Notches 30 are provided primarily to facilitate assembly of the transformer so that the arms 6 of yoke 2 may be forced apart by any suitable tool means. Projections 32 are also desirable in constructions wherein the entire assembly is located within an enclosing housing (not shown) such as a sheet metal housing, wherein the projections 32 engage one side of the enclosing housing and definitely space the core from the wall of the housing which it engages. Thereafter, if desired, the opening between the sideof the housing and the side of the core may be filled with pitch or other suitable insulating material. It is obvious that by blanking projections 32 in a tandem arrangement so that they project into the projections 10 of the adjacent core punching to form notches 30 no punching scrap will result. Further, as winding leg 8 is located in the middle of the yoke 2, the only punching scrap is the area between the winding leg 8 and the yoke 2. However, as projections 24A and 24B are required, as hereinafter described, it is obvious that in order to provide such projections such punching scrap would be i i single gap permits the use of larger tolerances on the single air gap whereby deformation of the laminations by the punch may be prevented.

Such advantages can be accomplished primarily because the longitudinal center line of the yoke 2 and winding leg 8 are coincident which permits the winding leg 8 to be rotated degrees about its longitudinal axis externally of the yoke 2 and relocated in the yoke 2 to form the finished core. Such rotation causes the upper projection 24B, as blanked, to be located adjacent, but spaced from, the lower arm 6 of the yoke 2 as shown in Fig. 4 and; conversely, so that the lower projection 24A, as blanked, is located adjacent, but spaced from, the upper arm 6 as shown in Fig. 4. Inasmuch as when initially fabricated the initial spacing between the projection 24B and the upper arm 6 of the yoke 2 provides the only spacing between the projections 24A and 24B and the upper and lower arms 6 of yoke 2, it is necessary that such initial spacing'must be equal to the total width of both air gaps when finally assembled. As the two air gaps are preferably equal, such initial spacing must be twice the desired air gap.

In order to obtain equal air gaps the projection 26 on the lower arm 6 must also extend transversely inwardly toward leg 8 a distance equal to the desired air gap, so that upon such rotation of the winding leg 8, projection 24B is spaced a distance equal to the desired air gap from the projection 26 and a distance equal to twice the desired air gap from the lower arm 6. Also, as projection 26 is equal in length of the spacing of the air gap, it will be seen that the projection 24A as initially blanked on winding leg 8 will be longer than projection 24B by a distance equal to the width of the desired air gap. Therefore, when projection 24A is rotated it will be spaced from the upper arm 6 of the yoke 2 a distance equal to the desired air gap. As shown, notches 36 and 38 may be provided on the winding leg 8 and the lower arm 6 of the yoke 2, respectively adjacent each side of the projections 24A and 26, respectively, for the purpose of facilitating manufacturing and are not a part of our invention. Accordingly, Fig. 4 of the drawings does not show the notches 36 and 38 as they are not essential to the operation of our core nor are they necessarily required in order to fabricate such a core. Similarly, in Fig. 2 it will be noted that bight portion 4 of yoke 2 is provided with an inwardly extending projection 40 on its inner side having a lateral width equal to that of winding leg 8 in order to facilitate the fabrication of the core. A corresponding offset 41 is provided on the outer edges of bight portion 4 for manufacturing purposes.

In order that the winding leg 8 may be removed from yoke 2, rotated about its longitudinal axis, and relocated between the arms 6 of yoke 2, the projection 12 and the single notch 14 are preferably located on the longitudinal center line of winding leg 8 and yoke 2, respectively, and they must be symmetrical with respect thereto. If desired, however, winding leg 8 could be constructed so that projection 12 could be located elsewhere at the end of leg 8 or a plurality of projections 12 could be provided as long as appropriate notches are provided in bight portion 4 to receive such projections upon rotation of the winding leg. Instead of the particular projection 12 and notch 14 shown, it is believed obvious that various other forms of interfitting configurations may be utilized. As shown in Fig. 2, a preferred configuration of projection 12 comprises longitudinally outwardly extending sides 42 from leg 8 which are joined together at their outer end by a symmetrical arcuate section 44. Notch '14 is of a complementary configuration to the projection 12. In order to facilitate assembly of the projection 12 in notch 14, after rotating winding leg 8 about its longitudinal center line, both projection 12 and notch 14 may be provided with a very slight taper outwardly.

It will be noted that the core lamination, shown in Fig. 3, is substantially identical in construction to the core lamination shown in Fig. 51, and, accordingly, like parts have been given the same reference number with a prime thereafter. The core lamination shown in Fig. 3 is modified from that shown in Fig. 1 in that its bight portion 4' is provided with a vertically extending elongated notch 14' in which the inner end of the winding leg 8' is located. As before, notch 14 may be provided with a very slight taper to facilitate the insertion of the winding leg 8'. It is believed obvious that this core can be fabricated in the same way as the one of Figs. 1, 2 and 4 to 6 and will function in substantially the same way. It should be realized, however, that this alternative construction is only one of many which may be employed for these purposes.

In assembling the complete transformer shown in Fig. 4, the yokes 2 of each lamination may be secured together in any suitable manner such as by providing aligned clearance openings 27 at each end of each arm 6 through which suitable fastening means such as machine screw and nut assemblies 28 may extend. A suitable opening 5 may also be provided in each leg 8 adjacent its end opposite the end from which projection 12 extends whereby all of the winding legs 8 may be readily fastened together. Further, an angled clamping plate 7 which may be fabricated from any suitable material such as sheet steel may be located at each side of the yokes 2, each of which extends between the opposed projections thereof, in order to clamp the winding legs 8 therebetween. Clamping plates 7 may readily be secured to yokes 2 by means of machine screw and nut assemblies 28 extending through openings therein which are in alignment with openings 27 of the yoke 2. When so assembled, it will be noted that, as shown in Fig. 6, the opposed edges of projections 10 firmly engage the opposite sides of winding leg 8. If desired, a notch 100 of any suitable configuration, such as a semicircle, may be located at the outer edge of winding legs 8 for identification purposes and to insure that all the winding legs 8 are properly aligned. When a notch 100 is utilized, the material therefor may readily be provided by an outwardly extending projection 101 on the outer side of the bight portion 4 of yoke 2.

As indicated, the transformer assembly is primarily adapted for controlling a negative resistance load which, as shown in Fig. 4, may comprise an instant start or a cold cathode discharge tube 50 of the fluorescent type having electrodes 52 at each of its ends. Electrodes 52, in turn, are electrically and mechanically connected to contacts 51 which extend outwardly of the tube 50 in a manner well known in the art and, accordingly, need not be more particularly described. In order to energize the transformer, coil 18 is electrically connected by means of suitable electrical conductors 54 and 56, which extend from' opposite ends of coil 18 to a source of suitable electrical energy such as the 118 volt systems commonly employed for such purposes. As shown, conductor 54 is connected to the conductor 22. Conductor 54- is also shown as being grounded by a ground connection 61 for certain safety precautions; however, if desired. either one of the supply conductors 54 or 56 could be so grounded or such ground connection may be eliminated without affecting the operation of the transformer assembly. As is also well known with the instant start type of lamp, grounded starting aids may be positioned adjacent the tube 50 in a manner well known in the art to facilitate starting of the tube 50. The secondary side of the circuit comprises a pair of electrical conductors 60 and 62 which are respectively connected to conductor 56 so as to be connected to one end of coil 18 and to the end of coil 20 opposite from that to which the conductor 22 is connected. Inasmuch as such connections may readily be made in any suitable manner well known in the art, such connections need not be more particularly described. Each conductor 60 and 62 is connected to a suitable lamp holder 64 for supporting the tube 50, which lamp holders may be of any suitable type for such purposes as are commonly available. As shown, each lamp holder 64 includes an electrical conducting terminal 65 of any suitable material such as copper or brass, one end of which is electrically engageable with one of the outwardly extending contacts 51 of lamp 50 and the other end of which is electrically connected to one of the conductors 60 and 62, respectively, in any suitable manner as is well known in the art. A condenser 68 is serially connected in conductor 62.

When the coil 18 is first connected to the source of energy, a magnetic flux flows through the winding leg 8, bight portion 4, arms 6 and projections 10 of the yoke 2 so as to couple the coil 18 to the coil 20 and induce a voltage therein. As the tube 50 is initially nonconducting, the secondary circuit is substantially an open circuit. Due to the high reluctance of the air gaps between the projections 24A and 24B and the arms 6 of yoke 2, before the ignition of the tube 50, little of the primary flux will flow through the shunts and, consequently, a secondary voltage substantially equal to the turn ratio voltage of the coils 18 and 20 will be applied to the tube 50 through the secondary circuit previously described. In order to obtain starting of the tube 50, the turn ratio voltage is chosen so as to effect breakdown of the gaseous atmosphere in tube 50 to render the tube 50 conducting, whereupon a substantial current immediately flows between the electrodes 52 of tube 50 through the secondary circuit previously described.

As soon as current flow begins in the secondary circuit, coil 20 produces a back magnetomotive force in the section of the core surrounding it which tends to oppose the flow of primary flux therethrough and, accordingly, a part of the primary flux is directed through the projections 24A and 24B so as to reduce the coupling bebetween coils 18 and 20, coil 20 has a high reactance which by proper design may be sufficient to permit coil 20 to function as a reactor which, with capacitor 68, will stabilize the operation of the negative resistance characteristic tube 50.

It will further be realized that the reactance of the coil 20 can also be varied by varying the reluctance of the entire core assembly. As heretofore described, the magnetic shunts provide only a fixed reactance for the coil 20; however, by means of projection 12 and notch 14, the reactance of coil 20 may be varied without eliminating the support for Winding leg 8 adjacent bight portion 4 of yoke 2. A variable reactance coil 20 is particularly desirable in manufacturing due to the capacitance tolerance on standard condensers such as condensers 68 with which coil 20 cooperates. Thus, as projection 2 has elongated sides 42, winding leg 8 may be moved longitudinally away from the bight portion 4 of yoke 2, as shown in Fig. 2, to provide an air gap between the inner side of the bight portion 4 and the side of the winding leg 8 adjacent thereto. As is well known, such an air ga increases the reluctance of the core assembly whereby the reactance of coil 20 is decreased. It will be noted that the winding leg 8 can be moved to various positions with reference to the yoke 2, with the inner end of winding leg 8 being supported by the engagement of the sides 42of projection 12 with the sides of the notch 14 at such various relative positions. It is obvious that such longitudinal movement of winding leg 8 is limited with relation to the cooperative length of projection 12 and notch '14; however, as only a small amount of such adjustment is necessary to obtain the desired variation in reactance of the coil 20, the cooperative length of projection 12 and notch 14 need not be of any great length. Further, as winding leg 8 is nominally only moved a small longitudinal distance, it will be obvious that the air gap between projection 24A and projection 26 will not be substantially effected. The air gap between projection 24B and the inner side of the upper arm 6 of yoke 2 will not be effected regardless of how far winding leg 8 is moved. Thus, it will be noted, that we have provided a core lamination which is normally provided with a high reactance section, which high reactance can further be varied over a range, as desired. Once the air gap between the bight portion 4 of yoke 2 and winding leg 8 has been established to obtain the desired reactance of coil 20, the air gap therebetween may be filled with any suitable non-magnetic material such as pressboard spacers to retain such desired air gap.

Although the core shown in Fig. 3 does not have the projection 12 and notch 14 as previously described, the cooperation of the winding leg 8 with the elongated notch 14 is similar to that previously described with relation to projection 12 and notch 14 and, accordingly, it. is not believed necessary to further describe such cooperation.

Having described a preferred embodiment of our invention in accordance with the patent statutes, it is desired that the invention be not limited to the specific construction shown and described, inasmuch as it is apparent that modifications thereof may be made without departing from the broad spirit and scope of our invention. Thus, for example, the magnetic shunts between the windings may be for-med entirely by aligned shunt portions which extend inwardly from the outer arms of the yoke toward the winding leg and by providing the winding leg with a cooperating projection similar to projection 26 or by,

aligned shunt portions which extend partially from the winding leg and the outer arm of the yoke. It is also obvious that such a transformer is suitable for use with other types of lamps rather than the cold cathode type of lamp described, although with such other lamps it is obvious that other control means and lamp holders may be necessary. Thus, for use with rapid start lamps it is obvious that the coils 18 and 26 could be provided with extensions or taps to provide heater windings for the electrodes of one or more lamps for such purposes. Accordingly, it is desired that the invention be interpreted as broadly as possible and that it be limited only as required by the prior art.

'We claim as our invention:

l l. A magnetic core lamination comprising separate yoke and winding leg members cooperable so as to define a magnetic flux path, a first portion of said yoke extending transversely across one end of said winding leg, an elongated projection extending longitudinally outwardly from said one end of said winding leg, said first portion of the yoke having a notch therein adapted to receive and support said projection for movement laterally with respect to said first portion and longitudinally of said winding leg, said notch and projection being engageable over an area which is substantially reduced upon'lateral movement of said winding leg away from said first portion, said notch and projection being of a length to support said winding leg upon the aforesaid lateral movement thereof to form a variable bridged air gap in said path, and said yoke member adjacent its other end having a portion engaging only the adjacent side of said winding leg member to guide the latter during its aforesaid longitudinal movement. 2. A magneticcore lamination comprising an elongated .U-shaped yoke having a. bight portion extending substantially perpendicular to each arm thereof, said arms being substantially the same length, a laterally in-' wardly extending first projection located at the free end of each of said arms, each of said first projections being substantially the same length and having their free ends spaced from the longitudinal center line of said yoke so as to be laterally spaced from each other, an elongated winding leg centrally located between said arms of said yoke and having one end closely adjacent the inner side of saidbight portion, said winding leg being engageable with each of said first projections at an area spaced from said one end so as to define a magnetic flux path in conjunction with said yoke, an elongated projection extending longitudinally outwardly from said one end of said wind-. ing leg, and said bight portion having a notch therein adapted to receive and support said projection therein for movement laterally with respect to said bight portion and longitudinally of said winding leg, said notch and projection being engageable over an area which is substantially reduced upon lateral movement of said winding leg away from said bight portion, and said notch and projection being of a length to support said winding leg during substantial lateral movement thereof as aforesaid to form a variable bridged air gap in said path.

3. A magnetic core lamination comprising an elongated U-shaped yoke having a bight portion extending substantially perpendicular to each arm thereof, said arms being substantially the same length, a laterally inwardly extending first projection located at the free end of each of said arms, each of said first projections being substantially the same length and having their free ends spaced from the longitudinal center line of said yoke so as to be laterally spaced from each other, an elongated winding leg centrally located between said arms of said yoke and having one end closely adjacent the inner side of said bight portion, said winding leg being engageable with each of said first projections at an area spaced from said one end so as to define a magnetic flux path in conjunction with said yoke, an elongated projection extending longitudinally outwardly from said one end of said winding leg on the longitudinal center line thereof, said longitudinal center line of said winding leg being coincident with the longitudinal center line 'of said yoke, said bight portion having a notch therein on the longitudinal center line of said yoke adapted to receive and support said projection therein for movement laterally with respect to said bight portion and longitudinally of said. winding leg, said notch and projection being engageable over an area which is substantially reduced upon the aforesaid lateral movement of said winding leg away from said bight portion, and said notch and projection being of a substantial length to support said winding leg upon the aforesaid lateraly movement thereof to form a variable bridged air gap in said path, a second projection extending laterally outwardly from each side of said winding leg between said bight portion and said first projections, a third projection extending laterally inwardly from one of said arms of said yoke, said second projections and third projection being substantially in lateral aligmnent, substantially equal gaps between said second projections and said third projection and said other'arm of the yoke, respectively, and one of said second projections beinglonger than the other by approximately the lateral length of said third projection. V

' 4. A magnetic core lamination comprising separate elongated yoke and winding leg members which are cooperable so as to define a magnetic fiux path, a first portion of said yoke extending transversely across one end of said winding leg, longitudinally extending interfitting means on said first portion of said yoke and said one end of said winding leg, respectively, for supporting said winding leg for lateral movement with respect to said first portion of said yoke and longitudinally of said winding leg member, said interfiting means being engageable over an area which is substantially reduced upon lateral movement of said winding leg away from said first portion, and said interfitting means being of a length to support said winding leg upon substantial lateral movement thereof as aforesaid to form a variable bridged air gap in said path.

5. A magnetic core lamination comprising separate yoke and winding leg members cooperable so as to define a magnetic flux path, a portion of said yoke extending transversely across one end of said winding leg, engageable cooperable means on said portion and said one end of said winding leg respectively, extending transversely to said portion and longitudinally of said winding leg for supporting said one end of said winding leg for movement in a path extending laterally with respect to said portion and longitudinally of the winding leg, said engageable cooperable means being engageable over an area which is substantially reduced upon movement of said winding leg away from said portion, and said cooperable means being of a length to support said winding leg during substantial longitudinal movement thereof to form a variable bridged air gap in said path.

6. A magnetic core lamination comprising a generally U-shaped yoke having a bight portion extending substantially perpendicular to each arm thereof, said arms being substantially the same length, an elongated winding leg centrally located between said arms of said yoke with one end thereof closely adjacent said bight portion, interfitting means on said bight portion and said one end of said winding leg, respectively, for supporting said winding leg with respect to said yoke, said interfitting means including means for forming a variable bridged air-gap between said yoke and said winding leg, a first projection extending laterally inwardly toward said winding leg from one of said arms, a second projection extending laterally outwardly from the side of said winding leg adjacent said one arm substantially in lateral alignment and substantially engageable with said first projection, a third projection extending laterally outwardly from the other side of said winding leg substantially in lateral alignment with said first and second projections, and said third projection being spaced from the other of said arms a distance substantially twice the length of said first projection so that when said winding leg is turned 180 about its central longitudinal axis there will be equal gaps between said second projections and said first projection and said other arm, respectively, of a length substantially equal to the lateral extent of said first projection.

7. A magnetic core lamination comprising a generally U-shaped yoke having a bight portion extending substantially perpendicular to each arm thereof, said arms being substantially the same length, an elongated winding leg centrally located between said arms of said yoke with one end thereof closely adjacent said bight portion, engageable cooperable means on said bight portion and said one end of said winding leg, respectively, extending transversely to said bight portion and longitudinally of said winding leg for supporting said one end of said winding leg for movement in a path extending laterally with respect to said bight portion and longitudinally of the winding leg, said engageable cooperable means being engageable over an area which is substantially reduced upon movement of said winding leg away from said bight portion, said cooperable means being of a length to support said winding leg during substantial longitudinal movement thereof to form a variable bridged air gap in said path, a first projection extending laterally inwardly toward said winding leg from one of said arms, a second projection extending laterally outwardly from the side of said winding leg adjacent said one arm substantially in lateral alignment and engageable with said first projection, a third projection extending laterally outwardly from the other side of said winding leg substantially in lateral alignment with said first and second projections, and said third projection being spaced from the other of said arms a distance substantially twice the length of said first projection so that when said winding leg is turned about its central longitudinal axis there will be equal gaps between said second projections and said first projection and said other arm, respectively, of a length substantially equal to the lateral extent of said first projection.

8. A magnetic core lamination comprising a generally U-shaped yoke having a bight portion extending substantially perpendicular to each arm thereof, said arms being substantially the same length, an elongated winding leg centrally located between said arms of said yoke with one end thereof closely adjacent said bight portion, an elongated notch in the inner side of said bight portion of said yoke having its open side disposed toward said one end of said winding leg and being of a size to receive said winding leg between the sides thereof, said one end of said winding leg being supported within said notch for movement in a path extending laterally with respect to said bight portion and longitudinally of the winding leg, said one end of said winding leg being engageable over an area of said notch which is substantially reduced upon movement of said winding leg away from said bight portion to form a variable bridged air gap in said path, a first projection extending laterally inwardly toward said winding leg from one of said arms, a second projection extending laterally outwardly from the side of said winding leg adjacent said one arm substantially in lateral alignment and engageable with said first projection, a third projection extending laterally outwardly from the other side of said winding leg substantially in lateral alignment with said first and second projections, said third projection being spaced from the other of said arms a distance at least somewhat greater than the lateral length of said first projection so that when said winding leg is turned 180 about its central longitudinal axis there will be equal gaps between said second projections and said first projection and said other arm, respectively, of a length substantially equal to the lateral extent of said first projection.

References Cited in the file of this patent UNITED STATES PATENTS 1,635,064 Wagner July 5, 1927 1,841,685 Sola Jan. 19, 1932 2,346,621 Sola Apr. 11, 1944 2,578,395 Brooks Dec. 11, 1951 2,582,291 Sola Jan. 15, 1952 2,646,552 Shingledecker July 21, 1953 2,712,618 Feinberg July 5, 1955 2,713,666 Henderson July 19, 1955 2,756,398 Feinberg July 24, 1956 2,790,960 Wyman Apr. 30, 1957 

